This invention relates to microscope sample holder supports and more particularly to a support for holding the filter pad on which particulate is to be viewed and focused through a programmed microscope to permit automatic focusing of the particles for analysis and counting.
In the art of microscopic particle analysis the particulate is deposited on a very thin filter pad in the form of a disk or wafer which is placed on a support at the microscope stage and held in place by mechanical rings which are positioned on the edge of the filter pad. Thus, the only portion of the filter pad that is held and maintained flat is the edge of the filter pad. State of the art high quality microscopes used as an image analyzer for particle counting can be programmed to move in three planes and has a limited depth of field automatic focusing capability in the Z-plane. When the microscope focuses on or "sees" a particle, it displays it on a screen where the size and number of particles can be made automatically. However, because of the limited depth of field of the automatic focusing features, if the filter pad on which the particles are carried is not planar, the microscope will not focus properly and thus will not see nor count the particles outside of its depth of field. Because the filter pads of the prior art were merely maintained flat at the peripheral edge, with the edge in focus, substantial portions of the remainder of the filter pads which are outside the focusing range could not be maintained. It has therefore been the practice in the prior art to manually focus the microscope in the Z-plane and manually refocus after the microscope has moved to a different point in the X-Y plane.